Electrostatic discharge (ESD) generated from static electricity is usually characterized by fast transient high voltage discharge. An ESD event can occur in electrical and electronic circuits, such as an integrated circuit (IC). It can create sufficiently high voltage to cause destructive breakdown of devices connected to, for example, the inputs and/or outputs of the integrated circuits.
In the case of bi-directional I/O drivers, which have mixed voltage signals, conventional ESD protection includes dual diode or MOS based circuits. Such conventional ESD protection results in leakage currents when the mixed voltage signal is above Vdd or below Vss.
An alternative approach is a silicon controlled rectifier (SCR) ESD protection circuit. However, SCR ESD protection circuits are subject to latch up during normal IC operation. Latch up affects the operation of the IC, rendering it defective.
Therefore, it is desirable to have an ESD protection circuit which can be quickly triggered to avoid damaging internal circuits and immune to latch up during normal operation.